Gram-negative bacillary sepsis with shock continues to have a high mortality rate. The pathophysiology and hemodynamic changes seen in gram-negative shock are etiologically related to endotoxin. Presently available methods to quantitate circulating endotoxin have been based on biological assay systems. A more direct approach would be to measure endotoxin rather than its biological effects. Based on the present knowledge of endotoxin structure and immunochemistry, assay systems dependent on immunoassay and/or quantitative biochemical extraction appear to be rational and feasible methods of detecting circulating endotoxin. The main objective of this investigation is to develop a sensitive assay for endotoxin utilizing the techniques of radioimmunoassay and labelled fatty acid. In vitro and in vivo experiments will be performed comparing the relative sensitivity and specificity of the radioimmunoassay and radiolabelled fatty acid techniques with that of the Limulus test. If these two techniques prove to be sensitive and specific, direct measurement of circulating endotoxin will be performed in patients with gram-negative sepsis. Correlation of severity of sepsis and quantity of circulating endotoxin will be attempted. In addition, the association of endotoxemia, as determined by the radioimmunoassay and radiolabelled fatty acid techniques, with bacteremia in patients with classical gram-negative bacillary sepsis will be ascertained.